Reciprocating internal combustion (IC) engines are known for converting chemical energy from a fuel supply into mechanical shaft power. A fuel-oxidizer mixture is received in a variable volume of an IC engine defined by a piston translating within a cylinder bore. The fuel-oxidizer mixture burns inside the variable volume to convert chemical energy in the mixture into heat. In turn, expansion of the combustion products within the variable volume performs work on the piston, which may be transferred to an output shaft of the IC engine.
Some constituents in the exhaust stream from an IC engine, such as, for example, nitrogen oxides (NOx), unburned hydrocarbons (UHCs), and particulate matter (PM), may be subject to government regulations. Accordingly, operators may wish to control concentrations of regulated exhaust constituents released to the environment. The composition of exhaust discharged from an IC engine may be affected by control of the combustion process within the variable volume main combustion chamber, exhaust aftertreatment downstream of the main combustion chamber, or combinations thereof.
Some IC engines employ an externally-powered ignition source to initiate combustion of the fuel-oxidizer mixture within the variable volume. For example, an IC engine may include a spark plug defining a spark gap between an anode and a cathode, where the spark gap is in fluid communication with the variable volume and in electrical communication with an electric potential. Accordingly, applying the electric potential across the spark gap may cause an electric spark to arc across the spark gap, thereby initiating combustion of the fuel-oxidizer mixture within the variable volume.
Some reciprocating engines may operate under “lean-burn” conditions, such that an overall fuel/oxidizer ratio of a fuel-oxidizer mixture within the main combustion chambers is less than the stoichiometric ratio. Stated differently, a lean-burn engine may operate with an excess amount of air with respect to a stoichiometric mixture, such that complete combustion of the fuel-lean mixture would result in combustion products including unreacted oxidizer but no fuel.
As a way to accelerate combustion and improve the reliability of ignition, some lean-burn engines may include a pre-chamber to initiate combustion of fuel-oxidizer mixtures in the main combustion chamber (see e.g., U.S. Pat. No. 7,261,097). In particular, the pre-chamber may be a relatively small chamber in fluid communication with the main combustion chamber, in which a fuel-oxidizer mixture is ignited by a spark plug. The ignited fuel-oxidizer mixture in the pre-chamber produces a flame which may jet out into the main combustion chamber to ignite the lean fuel-oxidizer mixture in the main combustion chamber.
However, there is a need for improved systems and methods for enhancing combustion stability in lean-burn engines, especially for developing engines to operate at fuel-oxidizer mixtures that are leaner that those conventionally employed. The present disclosure addresses the aforementioned problems and/or other problems in the art.
It will be appreciated that this background description has been created to aid the reader, and is not to be taken as a concession that any of the indicated problems were themselves known in the art.